Mercury in the 7th house represents the need to collect and impart information to others. Hence, this is why such a placement can do well in partnerships, counseling, receiving, and giving feedback. Those with Mercury here may want to convey an image to the public of being knowledgeable in their field, and someone who is well-informed in their area of expertise. The planet Mercury, when placed in the sphere of relating, may need to analyze and discuss relationships themselves. Alternatively, the individual will often be involved in verbal exchanges, debating, and sharing information. There is also sometimes a strong aptitude for psychology and understanding how others mentally tick. Ultimately, they like to have an audience to receive their ideas and will often appreciate verbal or written presentations by others.
Generally, a 7th house Mercury has a great interest in people, and this often results in an understanding of what the public finds interesting and their awareness and concerns. Such an individual may speak on behalf of others, and this is an excellent combination for those who work in mediation. It is an indicator of someone who excels at public relations or some kind of agency work, and they are often successful in law, sales, or advice. It is through their connection with others that leads to being mentally stimulated, and they want to help or advise other people with their problems. Above all, Mercury here needs intellectual stimulation in relationships, and they’re drawn to intelligent and verbal people, with whom they can share their academic interests, and who they can learn.
According to The Plain Vanilla Astrologer
People with Mercury in the 7th house usually seek mentally stimulating relationships. Sometimes the partner is a Mercurial type, having this planet (or Gemini and Virgo emphasized) in the chart. Occasionally the partner may be highly strung or even mentally unstable (particularly with afflictions from Uranus or Neptune or Pluto). Initially the attraction is likely to be towards the partner’s mental creativity, the stimulating companionship he or she provides, and the combined exchange of ideas. The individual may be seeking an intellectual as a partner in order to fulfill his or her neglected abilities in this direction. A 7th house Mercury also indicates that the individual may require constant change and variety in his (or her) relationship. So Mercury in this position is not always the best indicator for long-term partnerships. Perhaps because of the eternal-child quality of this planet, the individual with a 7th house Mercury sometimes has a much younger partner. However, the usual qualities of the partner, and sometimes to the fact that he or she is involved in journalism or education, for instance, two professions typical of Mercury.
If Mercury in the 7th house has no mental self-confidence in their own ideas and opinions they will let someone else do the thinking for them. They may even see others as being more intelligent and articulate than themselves. Planets in the 7th house can sometimes be given away to others, either consciously or unconsciously, as this sphere also rules our projections. Therefore, those with Mercury here are very concerned about what others think and will always seek mental companionship.
Howards Sasportas says,
With Mercury in the 7th, many problems can be ‘worked through’ if they are discussed and analyzed. Some people with this placement may be fairly (or should I say ‘unfairly’?) critical and judgmental about ‘those little things’ which their partner’s do which annoy them. Fortunately, the antics of the god of Mercury remind us that a sense of humor about such things is the great balancer.
Those with Mercury in the 7th house can arouse interest from the public to the subject at hand. They can be vital in playing an intermediary role in helping people with information. Similarly, they have a lot to learn through their contact with others and being drawn to environments where people talk, share, and exchange ideas. Either way, there is much to learn, teach, and communicate, and the ability to speak, write, and develop communication with others needs to be cultivated.